The present invention relates to a sliding plate and more specifically to a sliding plate for guiding material under test that includes a Venturi device disposed to produce a suction force using pressurized air.
Such a sliding plate is preferably used to ascertain the thickness measurement of a moved material under test, such as a paper web, where the distance of a target, e.g. a ferrite core is located, on the material under test or floating on an air cushion, respectively. The ferrite core is sensed by means of an oscillator coil arranged below the material under test within a cut-out of the sliding plate so that a measurement of the thickness of the material under test results. In order to provide selected conditions of web trajectory as smooth as possible, the material under test is kept adjoining the sliding plate at its passage by means of a suction device. Herewith the suction device comprises a Venturi nozzle outside of the sliding plate, whereat the vacuum produced by the Venturi nozzle via hose pipes and bores is connected to the surface of the sliding plate. Such a device is taught by German Patent DE 37 29 318 C2. Herewith it has proved to be disadvantageous that via those bores and hose pipes not only air, but also dust is sucked-in. In order to prevent clogging, pressurized air therefor has been periodically fed in a reverse direction to the hose pipe and bores.